The invention described herein relates generally to apparatus for providing a vacuum-to-air interface, and more particularly a high-powered pulsed particle beam vacuum-to-air interface capable of operating continuously at a high repetition rate.
Particle accelerators that are presently being designed and constructed will continuously provide extended sequences of high-powered particle pulses for long periods of time. As an example, the Advanced Test Accelerator (ATA) of the Lawrence Livermore National Laboratory will typically provide a 10,000 ampere, 50 MeV particle energy, electron beam emitted as individual 70 nanosecond full width at half maximum amplitude pulses occurring at a repetition rate of 1 Hz. In many of these new accelerators it will be necessary for the pulsed particle beam to pass from a region of near vacuum within the accelerator, such as at approximately 10.sup.-5 torr in the case of the ATA, directly into air at atmospheric pressure. In addition to maintaining the near vacuum within these machines at or below an acceptable pressure level, it will also be essential that the vacuum-to-air interfaces of the new accelerators not significantly alter any of the characteristic parameters of the individual pulses of the pulsed particle beams. Particularly because each of the particle pulses provided by these new accelerators will possess vastly more than enough energy to vaporize or disintegrate any material foil through which it passes, none of the presently known particle accelerator vacuum-to-air interfaces will be adequate for usage on the new machines.
As an example of a known particle accelerator vacuum-to-air interface, Luce, in U.S. Pat. No. 3,778,655 issued Dec. 11, 1973, describes a composite metal foil exit window for use in situations where atomic particles generated in an evacuated stucture are passed into a chemically reactive environment. The foil windows that are described would be ruptured by the individual particle pulses of a high-powered pulsed beam particle accelerator, such as the ATA, and thus could not provide vacuum protection for the interior of the accelerator.
Similarly, Farrel in U.S. Pat. No. 4,333,036 issued June 1, 1982 teaches an improved foil support for the exit window of a particle accelerator. Again, the foil window that is described would be ruptured by the high-powered particle pulses provided by continuously operating accelerators such as the ATA, and is thus not suitable for providing accelerator vacuum protection for machines of that type.
As another example of the prior art, Schlitt in U.S. Pat. No. 4,162,432 issued July 24, 1979, describes a metal foil perhaps 10 microns thick that comprises an interface for electrons in a relatively low-powered, repetitively pulsed electron beam machine. As in the two previous situations, this foil would be easily ruptured by the individual, high-powered particle pulser of accelerators such as the ATA, and thus could not provide vacuum protection for such high-powered machines.
Thus the problem remains of how to provide a vacuum-to-air interface, for a continuously operating high-powered pulsed particle beam accelerator, that maintains the vacuum level within the machine while, at the same time, not significantly altering any of the characteristic parameters of the individual particle pulses of the beam.